We develop a broadly applicable approach that drastically increases the ability to predict the properties of complex atoms accurately. We apply it to the case of Ir^{17+}, which is of particular ...interest for the development of novel atomic clocks with a high sensitivity to the variation of the fine-structure constant and to dark matter searches. In general, clock transitions are weak and very difficult to identify without accurate theoretical predictions. In the case of Ir^{17+}, even stronger electric-dipole (E1) transitions have eluded observation despite years of effort, raising the possibility that the theoretical predictions are grossly wrong. In this work, we provide accurate predictions of the transition wavelengths and E1 transition rates for Ir^{17+}. Our results explain the lack of observations of the E1 transitions and provide a pathway toward the detection of clock transitions. The computational advances we demonstrate in this work are widely applicable to most elements in the periodic table and will allow us to solve numerous problems in atomic physics, astrophysics, and plasma physics.
Hexagonal boron nitride (h-BN) nanosheets, spherical W nanoparticles, and their combinations were utilized as lubricant additives to synthetic PAO6 oil. The addition of W NPs led to a decrease in the ...coefficient of friction and wear rate. Molecular dynamics (MD) simulations and in situ TEM mechanical tests showed that the positive effect of adding spherical W NPs can be attributed to their rolling and sliding in the tribological contact zone. Adding BN nanosheets to PAO6 also improved the tribological performance of friction pairs: MD simulations suggest that the exfoliation and sliding of BN layers under tribological contact can contribute to the reduction of friction and wear. Moreover, a synergistic effect from the simultaneous addition of W and BN nanoparticles was observed: the CoF and wear reached minimum values among all tested suspensions. The formation of W/BN core/shell structures by wrapping of W nanoparticles by h-BN sheets provided superior macroscale lubricity.
•h-BN nanosheets and spherical W nanoparticles are studied as additives to PAO6 oil.•Adding W and BN NPs leads to a decrease in the friction coefficient and wear rate.•Exfoliation and sliding of h-BN NPs contribute to friction and wear reduction.•W NPs can withstand a high applied load and slide or rotate in the direction of applied load.•Formation of W/BN core/shell structures provides superior macroscale lubricity.
In slow collisions of two bare nuclei with the total charge number larger than the critical value, Zcr ≈ 173, the initially neutral vacuum can spontaneously decay into the charged vacuum and two ...positrons. Detection of the spontaneous emission of positrons would be the direct evidence of this fundamental phenomenon. However, the spontaneous emission is generally masked by the dynamical positron emission, which is induced by a strong time-dependent electric field created by the colliding nuclei. In our recent paper I. A. Maltsev et al., Phys. Rev. Lett. 123, 113401 (2019) it has been shown that the spontaneous pair production can be observed via measurements of the pair-production probabilities for a given set of nuclear trajectories. In the present paper, we have significantly advanced this study by exploring additional aspects of the process we are interested in. We calculate the positron energy spectra and find that these spectra can give a clear signature of the transition from the subcritical to the supercritical regime. It is found that focusing on a part of the positron spectrum, which accounts for the energy region where the spontaneously created positrons can contribute, allows us to get a much stronger evidence of the transition to the supercritical mode, making it very well pronounced in collisions, for example, of two uranium nuclei. The possibility of extending this study to collisions of bare nuclei with neutral atoms is also considered. The probability of a vacancy in the lowest-energy state of a quasimolecule which is formed in collisions of a bare U nucleus with neutral U and Cm atoms has been calculated. The relatively large values of this probability make such collisions suitable for observing the vacuum decay.
VISUAL ANALYSIS OF TIME-VARYING MULTIDIMENSIONAL DATA SETS Bondarev, A. E.
International archives of the photogrammetry, remote sensing and spatial information sciences.,
05/2023, Letnik:
XLVIII-2/W3-2023
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
This paper contains a description of computational experiments on the application of elastic maps to the analysis of time-varying volumes of textual information. Elastic maps are considered as a tool ...to provide analytical work with textual information and large information arrays of data. This paper presents the results of numerical experiments on the study of data volumes consisting of frequencies of joint use of words from different parts of speech, for instance “noun + verb” or “adjective + noun”. We consider text collections in Russian for experiments. Previously, static information arrays were mostly considered. It is for them methods of data analysis and methods of visual analytics were developed. Nevertheless, data comes in all the time in various areas of human activity. And in practice it is necessary to know how the cluster picture of multidimensional data volume changes over time. The paper describes the numerical experiments for real time-varying multidimensional data sets. Such experiments allows to analyze the evolution of cluster structure for multidimensional data and to trace the evolution for separate cluster.
Using specific examples, we constructively show that, in dimensions greater than
, the Lyapunov extreme instability of a differential system, i.e., the property that the phase curves of all nonzero ...solutions starting sufficiently close to zero leave any prescribed compact set, does not imply that these solutions go arbitrarily far away from zero in the sense of Perron or in the upper-limit sense as
. Namely, we construct two Lyapunov extremely unstable systems such that all solutions of the first system tend to zero, while the solutions of the second system are divided into two types: all nonzero solutions starting in the closed unit ball tend to infinity in norm, and all the other solutions tend to zero. Further, both systems constructed in the paper have zero first approximation along the zero solution.
It is constructively proved that the complete Perron and upper-limit instability (in contrast to the Lyapunov instability) of a two-dimensional differential system, generally speaking, does not imply ...its global instability. Moreover, the example of a completely unstable smooth nonlinear system constructed in this paper, in addition, has zero first approximation (along the zero solution) and not just partial but even massive partial stability.
Using a particular example, we constructively prove that the convergence of all solutions of a nonautonomous two-dimensional differential system to zero at infinity does not in general imply even the ...partial Lyapunov stability of the zero solution, because it may happen that each of the nonzero solutions at least once moves sufficiently far away from zero. In addition, the nonlinear system constructed in the present paper has zero first approximation along the zero solution.
In a separable Hilbert space, a smoothly solvable linear variational parabolic equation with a periodic condition on the solution is solved approximately by the projective-difference method. The ...discretization of the problem in space is carried out by the Galerkin method, and in time, using the Crank–Nicolson scheme. In this paper, time- and space-efficient estimates are established in strong norms of the errors of approximate solutions. These estimates permit one to obtain the rate of convergence of the error in time to zero up to the second order. In addition, the error estimates take into account the approximation properties of the projection subspaces; this is illustrated using subspaces of the finite element type.
Using the projection-difference method, we construct an approximate solution of an abstract linear parabolic equation in a separable Hilbert space with a periodic condition for a solution. We use the ...Galerkin method for the spatial variables and the implicit Euler discretization for time. We obtain root mean square estimates of the error of approximate solutions that are effective both in time and spatial variables; these estimates imply the convergence of approximate solutions to an exact solution and allow one to find the convergence rate.
The offshore and coastal infrastructure needs additional protection from wear, corrosion, and tribocorrosion. Herein, electrospark deposition (ESD) was employed to deposit composite TaC-(Fe,Mo,Ni) ...and (Ta,Zr)C-(Fe,Mo,Ni) coatings with a metallic matrix (similar in elemental composition to that of stainless steel) reinforced with carbide nanoparticles. The coatings were produced using TaC–Mo–Ni and TaC–ZrC–Mo–Ni electrodes under different energy regimes by varying frequency, voltage, and pulse duration to obtain different carbide contents. The obtained coatings have a bilayer composite structure: core-shell TaC–ZrC crystallites embedded in an Fe-based metal matrix with a (Ta,Zr)C network (zone 1) and approximately 5 nm Fe-based nanocrystallites surrounded by amorphous interlayers (zone 2). The tribological properties of TaC-(Fe,Mo,Ni) and (Ta,Zr)C-(Fe,Mo,Ni) coatings were superior to those of uncoated AISI 304 stainless steel, both in the 3.5% NaCl solution and in 3.5% NaCl + SiC suspension. The electrochemical characteristics of the best coatings were comparable to those of the stainless steel. Tribocorrosion tests indicated that when load is applied, the open-circuit potential values of steel reduce more significantly than those of the coatings.
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•Composite Ta(Zr)C-(Fe,Mo,Ni) coatings obtained by electrospark deposition in vacuum.•Carbide grains with core-shell structure: Zr-rich core, Ta-rich shell.•Coatings with enhanced tribological properties in 3.5% NaCl and SiC suspension.•In stationary corrosion Ta(Zr)C carbides protect Fe-based matrix.•At polarization, corrosion is determined by dissolution of more active matrix phase.
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